Benzoic acid undergoes dimerisation in Benzene solution. The Van’t Hoff factor(i) is

$2C_6{H}_{5}COOH\rightleftharpoons {\left(C_6{H}_{5}COOH\right)}_2$
 Before association  $\Rightarrow$ 1 mol
After association   $\Rightarrow 1-x$
Total $=1-x+\raisebox{1ex}{$x$}\!\left/ \!\raisebox{-1ex}{$2$}\right.=1-\raisebox{1ex}{$x$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$ 
$i=\frac{1-\raisebox{1ex}{$x$}\!\left/ \!\raisebox{-1ex}{$2$}\right.}{1}=1-\raisebox{1ex}{$x$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$